The Role of Fecal Occult Blood Testing in Screening for Colorectal Cancer COLORECTAL CANCER: AN UPDATE FOR DIAGNOSIS AND PREVENTION, SERIES

20 THE AVAILABLE FECAL OCCULT BLOOD TESTS— THE GUAIAC TESTS (GT) In 1985, Simon published an excellent review of FOBT testing for colorectal cancer (11). He stated that the concept of occult blood detection is generally credited to Van Deen, who in 1864 used gum guaiac, as an indicator reagent. Boas was the first to demonstrate its value for the detection of bowel malignancy (12) and Greegor was the first to stimulate interest in screening with the guaiac test (13). The guaiac FOBTs (GT) detect the peroxidase activity of heme either as intact hemoglobin or free heme. In the presence of heme and a developer (hydrogen peroxide) guaiac acid is oxidized producing a blue color. In screening for colorectal neoplasms a true positive GT is one which indicates bleeding from a colon cancer or polyp. All other positive results are considered to be false positive. Heme is present in red meat and peroxidase activity is present in fresh fruits and vegetables such as radishes, turnips and broccoli. These foods, therefore, have the potential to produce false-positive results. Some reports suggest that delaying development of GT cards for at least three days will decrease the number of false positives due to plant peroxidases and obviate the need for diet restriction of The Role of Fecal Occult Blood Testing in Screening for Colorectal Cancer COLORECTAL CANCER: AN UPDATE FOR DIAGNOSIS AND PREVENTION, SERIES #3